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bundles config is useful if doing a build and that build target was not an existing module ID, or if you have loader plugin resources in built JS files that should not be loaded by the loader plugin. Note that the keys and values are module IDs , not path segments. They are absolute module IDs, not a module ID prefix like paths config or map config . Also, bundle config is different from map config in that map config is a one-to-one module ID relationship, where bundle config is for pointing multiple module IDs to a bundle's module ID.